Liquid boron containing products



United States Patent LIQUID BORON CONTAINING PRODUCTS George F. Huff,Fox Chapel, and James D. Kliclrer, Mars, Pa., assignors to GalleryChemical Corporation, Pittsburgh, Pa., a corporation of Pennsylvania NoDrawing. Filed Oct. 24, 1957, Ser. No. 692,030

'4 Claims. (Cl. 52-.5)

This invention relates to the preparation of liquid products containingthe elements boron (B), carbon (C), and hydrogen (H) where at least partof the hydrogen is active hydrogen and in particular it concerns theproduction of such products 'by reactions of tetraborane (B H andunstable pentaborane (B H with a lower alkyl diborane.

It is an object of the present invention to provide a process for thepreparation of liquid products from the unstable boron hydrides,tetraborane and pentaborane-ll, and a lower alkyl diborane.

It is another object of the invention to provide a process according tothe foregoing object that is simple and that may be readily practicedwith known techniques.

We have discovered, and it is on this discovery that the invention is inlarge part predicated, that the unstable boron hydrides tetraborane andpentaborane-ll will react readily with a lower alkyl diborane to producea liquid reaction product. The product obtained is characterized bystability and a higher boron content than the alkyl diborane reactant.Consequently, it is apparent that our invention provides a convenientmethod of converting the inherently unstable boron hydrides, tetraboraneand pentaborane-ll, to a stable form that, as will appear hereinafter,is of significant utility.

The alkyldiboranes that are contemplated for use in this invention havethe general formula B H ,,R where x is a number from 1 to 4 and R is alower alkyl radical. Typical members of these alkyl diboranes includeethyl diborane, diethyl diborane, triethyl diborane, tetraethyldiborane, mono-, di-, tri-, and tetra-propyl diboranes, mono-, di-,tri-, and tetrabutyl diboranes, and so on. Mixtures of lower alkyldiboranes also can be used in our invention and constitute the preferredmaterial for economic reasons. A particularly satisfactory mixture ofalkyldiboranes that can be used is the liquid reaction product disclosedin the co-pending application of Schechter et al., Serial No. 402,805,filed January 7, 1954. That product consists essentially of mixtures oflower alkyl substituted diboranes, the alkyl radical dependingprimarily, of course, on the hydrocarbon used. Such liquids contain fromabout 70 to 98 weight percent of lower alkyldiboranes with the remainderbeing essentially alkylated higher boranes. The impure mixture can beused as such for we have found that the other materials present do notinterfere with obtaining our desired objects. Typical liquid productsproduced by the Schechter et a1. process have consisted essentially oftetraethyldiboranes, whereas others have included mono-, diandtriethyl-dib oranes. As noted in the Schechter et al. application, thosealkyldiboranes result upon reacting diborane and an unsaturatedaliphatic hydrocarbon containing up to about 6 carbon atoms such, forexample, as acetylene, ethylene, propylene, butylene, butadiene, ormixtures of such hydrocarbons, using a molar ratio of hydrocarbon todiborane not exceeding about 6 to 1, and suitably on the order of 1 to 1or 2 to 1. Where more than 6 moles of the hydrocarbon per mole ofdiboraue Patented Jan. 17, 1961 ICC are used, the product is an alkyl.boron, e.g., boron trialkyl, rather than a diborane derivative. Thatreaction can be carried out at temperatures up to about 150 C. whileusing atmospheric or superatmospheric pressure. The liquid reactionproduct as such, or a particular fraction containing an alkyldiboraneand obtained, for example, by fractionation of the crude product may beused in the practice of this invention. While the mixtures of loweralkyldiboranes that are obtained in accordance with the Schechter et al.process are preferred, if desired other mixtures containing particularalkyldiboranes in any desired predetermined proportions can be prepared,as by mixing the single members, and be used in practicing our inventionwithout departing from its scope.

Our invention is carried out by reacting tetraborane, unstablepentaborane, or mixtures of tetraborane and unstable pentaborane with atleast one lower alkyl diborane. Suitably up to about 35 percent byweight, based on the weight of the alkyldiborane, of the boron hydrideis used. The reaction can be carried out at ambient conditions, underrefrigeration to about -40 C., or at elevated temperatures, though veryhigh temperatures should be avoided because they will acceleratedecomposition of the boron hydride reactants thereby complicating theproblem of retaining the hydride. Consequently, it is desirable, thoughnot critical, that the temperature does not exceed about C. Reactionoccurs at atmospheric pressure as well as under elevated pressure orsub-atmospheric pressure. Pressure does not have a material effect onthe reaction and is utilized primarily to control the reactants.Generally, Where the higher temperatures are used, We prefer to keep themixture under autogenous pressure to avoid loss of the hydride.Accordingly, the reactants can be mixed at room temperature andatmospheric pressure and allowed to stand until sufficient reaction hasoccurred. Or the mixture can be formed at room temperature andatmospheric pressure in an autoclave or other closed reaction vessel andheated to expedite reaction. Also the reactants can be mixed at lowtemperatures, i.e. liquid nitrogen temperature (196 C.), and atmosphericpressure and then be permitted to stand whereupon the mixture reactswhile heating to ambient temperature. Where a vacuum is used, it isdesirable to operate below room temperature, at least for mixingpurposes, to minimize handling difficulties with respect to the boronhydride used. As will be apparent to the artisan, the time of reactionis not of significance, since some yield is obtained in any finite time.Reactions in accordance with our invention have been carried out in afew minutes and others have extended for days without detriment to thedesired results.

The invention will be described further by means of the followingexamples. It is to be understood that the details disclosed are given byway of illustration and are not to be construed as limiting theinvention.

Example I 5.3 grams of tetraborane were distilled into 8.5 grams ofethyldiboranes, containing mainly diethyl diborane, in an autoclave andthe mixture was heated to 58 C. for 44 hours. The resulting product wasthen distilled and diborane, unreacted tetraborane, and unreacted ethyldiboranes were removed. The liquid product which remained in the stillpot was analyzed and found to contain 54.4% boron by weight andcontained 52% of the boron originally charged to the autoclave. Aninfra-red spectrum of this liquid was characteristic of ethylsubstituted decaboranes. The refractive index of the liquid product wasn =1.5364.

The liquid products obtained in accordance with our invention areparticularly useful as fuels because they exhibit high heats ofcombustion. The heat of combustion of the product is substantiallydirectly proportional to its boron content. Accordingly, where a productis obtained having a higher boron content than the starting material, itis apparent that the resulting product has the higher heat of combustionand an upgrading of the starting material for fuel purposes hasoccurred.

Considering the foregoing facts in conjunction with Example I above, itcan be observed that the resulting liquid has a significantly higherpercentage of boron (54.4%) than does the starting diethyldiborane(about 25 weight percent B). Therefore, the product is a far better fuelthan the diethyldiborane. Furthermore, this product was obtained by useof the unstable boron hydride, tetraborane, and constitutes an efficientutilization of the material whereby it is converted to a stable form. Itshould be understood that the usefulness of the resulting products isnot affected by their purity. Consequently, where the volatility orsimilar requirements of the contemplated use permit, the product neednot be resolved to remove the unreacted components. 011 the other hand,if a particular fraction is needed the product can be resolved bydistillation, fractional crystallization or other conventional process.

In like manner and under substantially the same conditions, the reactionof pentaborane-ll and diethyldiborane resulted in a liquid producthaving a higher boron content, and therefore a higher heat ofcombustion, than the alkyldiborane used.

As noted above, the invention can also be practiced with a crude mixtureconsisting essentially of lower alkyl diboranes. The following exampleillustrates that embodiment of the invention.

Example II A liquid product that had been prepared by reacting acetyleneand ethylene with diborane by circulating gas streams of each of theforegoing through a packed column heated to a temperature of of about 80C. was used in this run. The hydrocarbons each were circulated at a rateof 25 mol per minute. The reaction extended for 8.2 hours. The resultingliquid reaction product was known, from routine analysis and previousexperience, to consist Of C2H5B2H5, (C2H5)2B2H4, (C H B H and (C H B HIt had a boron content of 26.7 mgm. a./g., expressed in milligramatomsper gram, boron, and 41.3 mgm. a./g. active hydrogen (hydrogenreleasable by hydrolysis of the composition). Tetraborane, in an amountof 3.9 percent by weight and at a temperature of l96 C., was mixed witha sample of the liquid alkyldiboranes in a closed vessel and theresulting mixture was allowed to warm to room temperature. Then a sampleof the mixture was analyzed and its boron content was found to haveincreased to 34.1 mgm. a./ g. and the active hydrogen increased to 57.0mgm. a./ g. This product was stored for 72 hours at room temperaturewithout any indication of decomposition.

Since it is known that tetraborane would be substantially decomposed in72 hours at room temperature, it is evident that the tetraborane reactedin the foregoing example and was tied-up or converted to a stable form.Analysis of the product disclosed that ethyldecaborane formed, thatbeing additional proof that reaction occurred.

As noted hereinbefore, an increase in boron content of such a liquidproduct is a direct measure of the improvement in the fuel value (heatof combustion) of the resulting product. The primary interest in thisdevelopment is the production of these materials for fuel uses.Accordingly, a large number of experiments of a qualitative nature wereconducted in order to obtain evidence of the best manner of preparingimproved fuels as evidenced by obtaining products with the highestpossible boron content.

Hence, a run substantially like Example II was made using 8.0 percent oftetraborane rather than the 3.9 percent of Example II. This run resultedin an increase in boron content from 26.0 mgm. a./g. to 35.4 mgm. a./g.and an increase in active hydrogen from 39.5 mgm. a./g. to 55.5 mgm.a./g.

In still another experiment with this general procedure (mixing at 196C. and allowing to heat to room temperature) but using 27.6 percent byweight of tetraborane, the boron content was increased from 25.7 mgm.a./g. to 47.3 mgm. a./g. while active hydrogen was increased from 37.3mgm. a./g. to 108.0 mgm. a./g. In these latter two tests .as with thatof Example II, the products were stored for 72 hours at room temperatureand found to be stable. Stability is, of course, direct evidence thatreaction occurred. However, it also is of economic importance since itshows that the products can be stored for later use or transported fromthe point of production to a distant point of use satisfactorily.

The foregoing runs .show, along with Example II, that there is arelationship between the boron content of the final product and thequantity of boron hydride used as a reactant. In general we have foundthat the greater the relative quantity of hydride used, the greater willbe the boron content of the resulting product.

The liquids resulting from our process have a variety of uses. As isreadily apparent from the hydrogen that is released upon hydrolysis, forexample dilute mineral acid hydrolysis, they constitute a convenient andportable source of hydrogen that does not require the unusual handlingand storage conditions associated with gaseous hydrogen. The productsalso are particularly useful as fuels in view of their high heat ofcombustion. They can be mixed with a conventional oxidizer, such as airor oxygen, and be burned in a space heater or other means that utilizesfuels. However, they are of particular interest as a fuel in abi-propellant system, primarily in turbo jet, ram jet and rocketengines. These fuels can be used alone or in mixtures with other fuelstoward which they are chemically inert, e.g. most ordinary hyrocarbonfuels. They are considered to be exceptionally suited to these purposesin view of their high heat of combustion (20 to 50 percent greater thanthe best hydrocarbon fuels); they are spontaneously flammable at hightemperature, have a low freezing point, a large liquidus range, and highdensity. In actual tests, a sample of the liquid product is introducedinto the combustion section of a jet test engine, burned with compressedair, and the efficiency of the combustion and the output of the enginemeasured. When a sample of a product such as is obtained in Example I isburned in a test engine, it has a heat of combustion more than about 20percent greater than the best hydrocarbon fuel. The combustionefficiency is equal to JP-4 (a standard jet fuel in use for severalyears past) and the thrust of engine per unit weight of fuel issubstantially greater than the thrust obtained using the besthydrocarbon fuels. In comparative tests on the fuel produced by theabove process and other boron-containing high energy fuels and otherhydrocarbon fuels, it has been found that engine output is directlyproportional to the heat of combustion per unit weight of fuel. Thus, anaircraft using a high energy boron-containing fuel can travelproportionately farther with the same load or can carry proportionatelygreater loads, than when burning conventional fuels.

This application is a continuation-in-part of our copending applicationSerial No. 429,115, filed May 11, 1954 and now abandoned.

In accordance with the provisions of the patent statutes we haveexplained the principle of our invention and have described what we nowbelieve to represent its best embodiments. However, we desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A method of increasing the boron content of a liquid consistingessentially of at least one lower alkyl diborane which comprises mixingand reaching a lower 5 6 alkyl diborane and a member selected from thegroup conselected from the group consisting of tetraborane, pentasistingof tetraborane, pentaborane-ll and mixtures borane-ll, and mixturesthereof, and recovering the rethereof, and recovering the resultingliquid reaction suiting liquid reaction product. product. 4. A methodof: improving the heat combustion of a 2. A method of improving the heatof combustion of a 5 liquid consisting essentially of at least one loweralkyl liquid mixture consisting essentially of lower alkyl diboranewhich comprises mixing and reacting lower alkyl diholahes whichcomprises mixing and reacting Such diborane with up to about 35 weightpercent of a member mixture with a member Selected from the groupconsist selected from the group consisting of tetraborane, pentaing oftetraborane, pentaborane-ll and mixtures thereof, borne. and mixtures thf at a temperature of up and recovering the resulting liquid Product 10to about 100 C. and recoverin the resultin 1i uid 3. A method ofimproving the heat of combustion of a reach-on product. g g q liquidmixture consisting essentially of ethyldiboranes which comprisesreacting such a mixture with a member No references cited.

ERNEST W. SWIDER UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTIONPatent No, 2,96i3,54 January 17, 1961 George F0 Huff et all,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4,, line 75 for "reaching" read reacting -==5 column 6, line 4,for "heat combustion" read we heat of combustion e Signed and sealedthis 27th day of June 1961o (SEAL) Attest:

DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATESPATENT oEFIcE (IERTIFICATION OF CORRECTION Patent Noe 2,96$,54O January17, 1961 George F., Huff et ale It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below;

Column 4, line 75, for "reaching" read reacting column 6, line 4, for"heat combustion" read heat of combustion Signed and sealed this 27thday of June 19610 C SEA L) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of PatentsPatent No., 2,966,540 January 17, 1961 George F0 Huff et ale It ishereby ceroified that error appears in the above numbered patentreqiiring correction and that the said Letters Patent should read ascorrected below'.

Column 4, line 75, for "reaching" read reacting column 6, line 4, for"heat combustion" read heat of combustion e,

Signed and sealed this 27th day of June 1961o (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. A METHOD OF INCREASING THE BORON CONTENT OF A LIQUID CONSISTINGESSENTIALLY OF AT LEAST ONE LOWER ALKYL DIBORANE WHICH COMPRISES MIXINGAND REACHING A LOWER ALKYL DIBORANE AND A MEMBER SELECTED FROM THE GROUPCONSISTING OF TETRABORANE, PENTABORANE-11 AND MIXTURES THEREOF, ANDRECOVERING THE RESULTING LIQUID REACTION PRODUCT.